One of the many uses of unmanned aerial vehicles (UAVs) is to capture video or other images taken by cameras on the UAVs. UAVs can have on-board still or video cameras capable of taking and storing the images in on-board memory. When the UAV lands, the user can then retrieve the images from the on-board memory to view the images, either by downloading the images from a memory card or simply removing a detachable memory card. Alternatively, the UAV can transfer image data to a ground terminal while mid-flight. The ground terminal typically is coupled to a computer that can display the images on a monitor. The ground terminal alternatively can be a mobile computing device (such as a mobile phone or tablet) that displays images on the mobile computing device's screen. In this way, a user can view the UAV images at the ground terminal in real-time.
Users generally control UAVs via a handheld remote control device. The remote control device sends flight control signals to the UAV. The remote control can also send to the UAV special control signals, for example, a signal to trigger the photo-taking or video-recording function of the camera. The handheld remote device can be a standalone remote control device or can be connected to a computer or mobile computing device at a ground terminal. Sophisticated ground terminal apparatuses are capable of displaying real-time status information about the UAV, displaying images captured by the UAV, and offering additional functions such as planning a flight route.
Technical challenges arise when a user wishes for the UAV to wirelessly transmit image data while in flight. Image data transmissions demand a great deal of bandwidth. Therefore, conventional UAVs typically provide a wireless channel for the flight control signals that is separate from the wireless channel for the image signals. A wireless channel is a frequency range centered about a particular frequency. For example, the 2.4 G Wireless Fidelity protocol operates at around 2.4 Gigahertz.
One disadvantage of a two-channel system is the increased bulk and complexity of the system. Two-channel systems require two separate transmitters, an image transmission device on the UAV and a remote flight control transmission device located at the ground terminal. A two-channel system also requires two receivers, an image reception device at the ground station and a flight control reception device on the UAV. Two-channel systems may be too cumbersome for a single user to easily operate. One person may need to operate the UAV, while another controls the camera. Current methods of transmitting image and remote data through a single channel have the disadvantage of high latency because of low bandwidth limitations. The disclosed embodiments improve latency by advantageously transmitting handshaking signals (such as acknowledgment signals) selectively. That is, not every transmission uses handshaking signals.